1. Field of the Invention
This invention relates to a method of processing the gradation of a mammogram and apparatus therefor, and more particularly to a method of and apparatus for processing the image gradation of a mammogram in a mammogram copying system in which an original mammogram is read out and recorded on a recording medium.
2. Description of the Prior Art
In the mammography, an X-ray film is generally used for recording the X-ray transmission image of the mamma. The mammogram is observed with the naked eyes or a magnifying glass for diagnosis. In the mammogram, there are recorded the glandular tissue, the subcutaneous tissue and the skin. The glandular tissue has the lowest density since the transmittance thereof to the X-rays is the lowest. The subcutaneous tissue has the second lowest density since the transmittance thereof to the X-rays is comparatively low. Blood vessels run in these tissues but have a low contrast since their X-ray absorption difference is very small. The skin has a high density since the transmittance thereof to the X-rays is high. The part outside the substantial image of the mamma has the upmost density since this part of the X-ray film is exposed to X-rays directly coming from the X-ray source.
As mentioned above, the mammogram has a wide range of density ranging from 0 to 3.5 in terms of optical density. Further, since the various parts are not recorded in the desirable contrast respectively, it is very difficult and necessary to have a great skill to make proper diagnosis from the mammogram in which the disease must be found out from a very slight variation in density in the image.
Then, the inventors of this invention have invented a radiographic image processing system in which a normal radiograph is used as an original image and is optically scanned and read, and the read out signal is processed by a signal processing means to change the various image properties such as contrast and the density level, and then the processed signal is used for reproducing an improved image on a copying film.
In the radiography, however, the recorded image is used for the purpose of "diagnosis" and the diagnostic efficiency and accuracy (the level of easiness for diagnosis of adaptability to diagnosis) are not simply enhanced by simply making so-called "good" image from the point of the ordinary image quality factors such as sharpness granularity and contrast. Rather than these factors, the diagnosis efficiency and accuracy are influenced by other complex factors such as reference with the normal pattern, reference with the anatomical structure and utilization of other diagnostic view or records.